238 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
is solved through the use of such apparatus as we have described 
using ultra-violet radiations. That of the sterilization of very great 
quantities of water, as in the case of a city’s supply, is now under study 
but very near solution by the same means. 
CAN ALL LIQUIDS BE STERILIZED BY THE ULTRA-VIOLET RAYS? 
To this question I must answer, No. With Th. Nogier, I have 
shown that substances rich in colloidal matter (wine, beer, cider, 
bouillon, peptonized solutions, etc.) absorb very rapidly the ultra- 
violet radiation.! This radiation will penetrate only a few millimeters 
or fractions of a millimeter of such liquids, which therefore are not 
sterilized. Even in the case of the most limpid beer, the clearest 
> 
es se femasiasins* iilisialsne wos 
% —_ Quarts Kare y 
\e ? 
Fic. 2.—Vessel holding 115 liters for experiments on the sterilization of water. 
white wine, a peptonized solution as transparent as water, steriliza- 
tion does not result. Indeed, such liquids may be sterilized in the 
laboratory either by exposing them in very thin layers or by stirring 
them so that every portion comes in contact with the lamp. The 
practical results of such methods are negligible; such sterilization 
would be too costly. 
The water for our method must be clear; a muddy water would 
not be sterilized. It would have to be filtered before entering our 
apparatus. 
And so clear water is practically the only known liquid permeable 
to the ultra-violet radiation and easily sterilized by it. 
1 J. Courmont et Th. Nogier, Sur la faible pénétration des rayons ultra-violets 4 travers les liquids conte- 
nant des substances colloides. Ac. des Sciences, 2 aofit 1909, 
